Eoss Granville Harrison 215 



swimming movement. These experiments afford therefore a corrobora- 

 tion of the conclusion drawn from experiments on higher animals that 

 the acetone-chloroform acts upon the nerve centers and not peripherally. 



The general retardation of the development of the drugged organisms 

 results probably in the first instance from disturbances in the metabolism 

 of the cells, possibly in their diminished power of oxidation. It is at 

 least justifiable to assume this in view of our knowledge of the action 

 of related substances, such as chloroform, upon adult organisms. While 

 the external gills of the embryo are functional, this is perhaps the sole 

 cause for the slower development. Later, when the internal gills are 

 developed, the larva, which are nornuilly dependent on the respiratory 

 movements for the proper aeration of the blood, must lack an adequate 

 supply of oxygen. This contributes to further delay in development 

 and no doubt is the cause of some of the deviations from the nornuil 

 course, which manifest themselves more clearly in this late period. 



The differences in external form between the normal and the drugged 

 embryos are not great. There is often a considerable effusion of fluid 

 into the pericardial cavity at an early period, causing an unusual swelling 

 in this region '(cf. Fig. 13 and Fig. 13) ; and besides, the bodies of the 

 drugged larvse are usually somewhat swollen. The caudal fin of these 

 specimens fails to expand as fully as in normal ones (cf. Fig. 14 and 

 Fig. 15). The oedema and the pericardial effusion are no doubt due to 

 weakened heart action, and this may affect also the circulation in the 

 tail to some extent, resulting in a slight arrest of development. The 

 vacuoles, wliich form in the axial sarcoplasm of the muscle hbers, may 

 also be accounted for by disturbances in the circulation. 



DlSCUSSIOX OF THE KeSULTS. 



In the first series of experiments described above, the spinal cord of 

 the embryo was removed before the histological differentiation in either 

 the muscular or the nervous tissue had begun. From the very beginning 

 of the visible changes in structure, which transform a simple meso- 

 dermal cell into a muscle fiber, tlie isolation of the musculature from the 

 nervous system was complete. All chance for tlie exertion of any pecu- 

 liar formative stimulus emanating from tlie nervous system as such was 

 eliminated ; and likewise, owing to the consequent paralysis of the mus- 

 cles in question, any possible stimulus resulting from the functional 

 activity of the muscle itself was excluded. Still the differentiation of 

 the contractile substance took place in normal manner, as did the group- 

 ing of the fibers into individual muscles. Just as Schaper's experiments 

 have shown that the brain as a nerve center exerts no general formative 



